Only real way is to start with a fresh install, backup data, boot from install CD. keep clicking next.
Just to cover all the bases only need to install it if you actually need to eg, more than 4GB RAM
I have 2gb ram can i go ahead and install? and while installing i see a message on the screen like input not support. And once the windows boot up it will disappear. what would be the reason for that..
The only reason to have a 64bit os is if your running more then 4gb of ram. Right now you have 2gb of ram and 32bit os, unless there is some special reason for wanting 64bit there is no need for it.